Effects of Structural Tuning of Hydrophobic Side Chains of Cognate Ionomers on Micro-Nano Pore-Filling Composite Anion Exchange Membranes and Their Electrodialysis Performance

Exploring the interplay between side-chain structures of ionomers and “active” micro/nanoporous substrates, along with its impact on the structure and performance of composite membranes, is beneficial for developing high-performance anion exchange membranes (AEMs) for electrodialysis desalination. Herein, a series of tandem di-cation ionomers with hydrophobic alkyl side chains of varied lengths were synthesized, and pore-filled composite AEMs were developed using ultrathin microporous polyethylene (PE) as substrate. The structural and functional properties of these composites were systematically studied benchmarking with their ionomer membranes. The results reveal that space binding of pore walls restricts water uptake and swelling of conductive phases in composites with short side chains (≤ 6 carbons), leading to marginally enhanced mechanical strength and ion selectivity but slightly reduced conductivity. Pore-filling with longer side-chain ionomers induces interface-induced assembly, improving the interface connection between the ionomers and substrate. The space binding and interface-induced assembly collectively change the ionomer phase structures of composites. Notably, QPT-C18@PE with the longest hydrophobic side chains achieves exceptional performance including 95.45% current efficiency, high salt flux (81.02 mg m⁻² s⁻¹), low energy consumption (1.61 kWh kg⁻¹ NaCl), and robust stability during electrodialysis. This work provides insights into designing advanced composite AEMs for efficient desalination applications.